Agriculture Reference
In-Depth Information
phate poisoning. Recovery depends ultimately on generation of new enzymes
in all critical tissues.
Organophosphates are efficiently absorbed by inhalation, ingestion, and skin
penetration. To a degree, the occurrence of poisoning depends on the rate at
which the pesticide is absorbed. Breakdown occurs chiefly by hydrolysis in
the liver; rates of hydrolysis vary widely from one compound to another.
Rarely, certain organophosphates have caused a different kind of neuro-
toxicity consisting of damage to the axons of peripheral and central nerves and
associated with inhibition of "neurotoxic esterase" (NTE). Manifestations have
been chiefly weakness or paralysis and paresthesia of the extremities, pre-
dominantly the legs, persistent for weeks to years. Most of these rare oc-
currences have followed an acute poisoning episode of the anticholinesterase
type, but some have not been preceded by acute poisoning. Only a few of the
many organophosphates used as pesticides have been implicated as causes of
delayed neuropathy in humans. EPA guidelines require that organophosphate
and carbamate compounds which are candidate pesticides be tested in suscepti-
ble animal species for this neurotoxic property.
Other specific properties of individual organophosphates may render them
more hazardous than basic toxicity data suggest. By-products can develop in
long-stored malathion which strongly inhibit the hepatic enzymes operative in
malathion degradation, thus enhancing its toxicity. Certain organophosphates
are exceptionally prone to storage in fat tissue, prolonging the need for anti-
dote as stored pesticide is released back into the circulation. Animal studies
have demonstrated potentiation of effect when two or more organophosphates
are absorbed simultaneously; enzymes critical to the degradation of one are
inhibited by the other. Whether this interaction is a significant factor in hu-
man poisonings is not known.
b.
N-Methyl Carbamate Insecticides
Table 5.4
lists current carbamate insecticides products. They are grouped
by the relative toxicities.
Table 5.4
Carbamate insecticides products grouped by relative toxicities.
Highly toxic*:
Moderately toxic*:
aldicarb
+
(Temik)
dioxacarb (Elocron, Famid)
oxamyl (Vydate L, DPX 1410)
promecarb (Carbamult)
methiocarb (Mesurol, Draza)
bufencarb (metalkamate, Bux)
carbofuran (Furadan, Curaterr, Crisfuran)
propoxur (aprocarb, Baygon)
isolan (Primin)
trimethacarb (Landrin, Broot)
methomyl (Lannate, Nudrin, Lanox),
pirimicarb (Pirimor, Abol, Aficida, Aphox,
Fernos, Rapid)
eormetanate (Carzol)
dimetan (Dimethan)
aminocarb (Matacil)
carbaryl (Sevin, Dicarbam)
